Was hauling a load to the dump, truck was driving fine. Stopped at a light, lost power and stalled. Didn't want to restart, when it did was running really rough,shuddering and I had to keep the RPMs up to keep it running. Moved it to a near by parking lot with very little power and unusual sound (clacking) coming from area of valve covers. Oil pressure dropped and I shut the truck down. All other gauges were fine. 2002 5.7 litre Ram 1500, Thoughts?